Friction properties of acrylic-carboxylated latex films—1: Effects of acrylic acid concentration and pH

The aim of this work was to investigate how specificities of thin films prepared from aqueous polymer colloids (latexes) influence their friction properties, tested with a sliding stainless steel spherical tip. Two acrylic latexes containing either 1 wt% or 4 wt% of acrylic acid (AA) were used at pH 2 or 10. Bulk mechanical properties were also studied in order to improve the interpretation of friction results. Increasing AA concentration and pH increases the overall film rigidity, pH being more effective than AA concentration. Contact pressures are directly correlated to bulk mechanical properties whereas surface shear stresses are also strongly influenced by molecular interactions with the sliding tip. Friction coefficients are rather high, peaking at 5, because of important viscoelastic dissipation in the films as well as strong polar interactions introduced by AA, especially at high pH. The paper also addresses the question of the relevant characteristic length in this kind of friction study.